The present invention relates to heating apparatus control devices and more particularly, to a duplex thermostat designed for use with a heating apparatus having two individually actuatable heating elements.
Thermostatic control devices of a variety of different configurations have long been known and used in the art to regulate heat producing apparatus. Such thermostats normally comprise a pair of relatively movable contracts which are electrically connected to make and break the energization circuit for the heating element or elements of heat producing apparatus. One of the contracts is operatively connected to a thermally deformable element, often in the form of a bimetallic strip, which deforms to move the contacts into engagement when the environmental or sensed temperature reaches a predetermined level. Some method is normally provided for setting and adjusting the desired temperature level. One simple method of accomplishing this result is by varying the distance between the contacts such that more or less deformation of the bimetallic strip is required before the contacts engage.
A conventional thermostat, as described above, has a significant disadvantage when utilized to control the actuation of a conventional heat producing apparatus. When the heating element or elements are initially energized, the environmental temperature rises rapidly towards the desired level. When the desired level is reached, the heat producing elements are deactuated. However, because of the nature of such a system, the environmental tempera- continues to rise significantly above the desired temperature, thereby initially "overshooting" its mark. As the environmental temperature decreases past the desired temperature level, the thermostat will again actuate the heating elements. However, before the environmental temperature begins to rise, it will decrease to a level somewhat below the desired temperature level, thereby "undershooting" the mark. Because there is a significant time lapse or lag between the time when the thermostat actuates (or deactuates) the heating apparatus and the time when the environmental temperature rises (or decreases) significantly, the environmental temperature will continually alternatively overshoot and undershoot the desired temperature level. The initial overshoot will be the largest, and the amplitude of the deviation will, after a few cycles, become substantially constant as the system enters a steady state condition. Thus, as time goes on, the environmental temperature will alternate cyclically around the desired temperature level. The amplitude of this cyclical differential between the environmental temperature and the desired temperature level, is significant, not only from the viewpoint of the comfort of individuals in the environment, but also from an energy conservation standpoint because a system with large cyclical variations requires more energy than necessary to control the environmental temperature.
It is, therefore, a prime object of the present invention to provide a duplex thermostat which, in conjunction with a two-element heat producing apparatus, is capable of significantly reducing the amplitude of the steady state cyclical variations of the environmental temperatures with respect to the desired temperature level.
It is another object of the present invention to provide a duplex thermostat which, in conjunction with a two-element heat producing apparatus, is capable of significantly reducing the initial overshoot of the environmental temperature with respect to the desired temperature when the heat producing apparatus is energized.
It is another object of the present invention to provide a duplex thermostat which is usable in conjunction with a two-element heating producing apparatus wherein the temperature difference .DELTA. t between the levels at which the respective heating elements are actuated can be adjusted and the entire device can be calibrated to set the desired temperature level.
It is still another object of the present invention to provide a duplex thermostat wherein the two thermostatic functions are combined into a single device which can be manufactured at a minimal cost.
It is still another object of the present invention to provide a duplex thermostat which consists of simple and inexpensive parts which function together reliably to perform the desired result.
In accordance with the present invention, a thermostat is provided, including a support to which first and second resilient members are mounted in spaced relation. Each of the members has mounted thereon a pair of contacts. Each of the contacts on one of the members is aligned with a different contact on the other member. A thermally deformable element, preferably in the form of a bimetallic strip, is mounted on the support at a point spaced from the first member. Means are provided which operably connect the deformable element with the first member such that deformation of the element moves the first member relative to the second member. Means are provided for adjustably positioning the second member relative to the first member in order to permit setting of the desired temperature level t.
The first member is formed of first and second electrically isolated parts, upon each of which is mounted one of the contacts. The second member, and thus the contacts carried thereby, are operatively connected to a circuit containing a source of energization for the heat producing apparatus. Each of the first and second isolated parts, which make up the first member, are operatively connected to a different one of different heating capacity heating elements. Thus, the heating elements are independently actuated when the contacts situated on the first member are respectively engaged with the aligned contacts on the second member. The means which connects the first member with the deformable element comprises individual means for spacing the first and second parts of the first member, respectively, different distances from the deformable element. Thus, the thermostat can be calibrated such that the heating elements will be actuated respectively at different degrees of deformation of the thermally deformable element.
The spacing means between the deformation element and first means takes the form of a pair of abutments mounted on the thermally deformable element. Preferably, at least one of the abutments is position adjustable with respect to the thermally deformable element, such that the difference in the degree of deformation of the thermally deformable element (and thus the difference in the respective temperatures at which the heating elements are actuated) required to cause engagement of the aligned sets of contacts, respectively, is also adjustable.
The result of this configuration is that the initial overshoot in the environmental temperature with respect to the set temperature level is substantially eliminated. Further, the amplitude of the steady state cylical variations of the environmental temperature around the desired temperature level is substantially reduced. Thus, the environmental temperature stays much closer to the desired temperature level than is possible with a conventional thermostat. Moreover, since intial overshoot is virtually eliminated and the amplitude of the cyclical variations in environmental temperature, as compared to the desired temperature level, is reduced, a conservation of energy resultss